Introduction
Vitamin E is the name given to a group of fat-soluble compounds, which include tocopherols and tocotrienols. The term “tocopherol” comes from the Greek word meaning “to bear offspring”. A Vitamin E deficiency in rats results in infertility and the re-introduction of Vitamin E to the diet corrects this problem. The most abundant and potent form of Vitamin E is d-alpha tocopherol (natural Vitamin E). Vitamin E is destroyed by light and oxygen. At the same time, however, it protects Vitamin A, Vitamin C and carotenes in food from oxidative destruction.
Absorption and Metabolism
As a fat-soluble nutrient, Vitamin E is absorbed from the intestinal tract via chylomicrons and lymph. It is carried in the blood by lipoproteins (i.e., VLDL and LDL) and is stored primarily in adipose tissue, with smaller amounts found in the liver, muscle tissue and adrenal glands.
Vitamin E is released into the circulation whenever fat is mobilized. Its metabolites are excreted both in urine and in feces.
Approximately 50 to 85 percent of Vitamin E is absorbed from the intestinal tract into the bloodstream, provided there is some fat present in the intestinal tract.
Recommended Daily Allowance (Vitamin E)
Equivalents
1 mg of d-alpha tocopherol (natural) = 1 alpha tocopheral equivalent (alpha T.E.) = 1.49 IU1
The “d” form denotes natural Vitamin E and is also known as RRR-alpha tocopherol.
The “dl” form denotes synthetic Vitamin E and is also known as all-race-alpha tocopherol.
Relative Biological Activity of Various Tocepherols2
N.B. In the human body, only the d-form is recognized (natural Vitamin E). Although the l-form has antioxidant activity, it may actually inhibit the d-form from entering cell membranes. Thus most authorities recommend supplementation using only natural Vitamin E (d-alpha-tocopherol).3,4,5 Recent studies suggest that natural Vitamin E is twice as bioactive as the synthetic form.6
Vitamin E Deficiency
Newborn infants have low tissue concentrations of Vitamin E because there is little transfer across the placenta. A haemolytic anemia can result in infants if their serum tocopherol levels are less than 0.5 mg/dl. A severe eye disorder called retrolental fibroplasia may also result.
This problem usually arises due to infant formulas high in polyunsaturated fats and containing iron. Because of formula changes, it is now rarely seen.
In adults Vitamin E deficiency can occur in:
Fat malabsorption syndromes, such as sprue, celiac disease, cystic fibrosis, and post-gastrectomy syndrome.
Sickle cell anemia and thalassemia.
Hemodialysis patients.
Symptoms of Vitamin E deficiency in adults include nerve damage, muscle weakness, poor coordination, involuntary movement of the eyes, red blood cell rupture leading to anemia (haemolytic anemia).
This suggests a neurological role for Vitamin E, in addition to its known antioxidant function.1,2,7
Functions
Antioxidant
As a fat-soluble antioxidant Vitamin E has been shown to protect various structures from oxidation and free radical damage, including:
a. LDL-cholesterol8
b. Cell Membrane structure9
c. Thymus gland10
d. White blood cells10
e. Lens and macula of the eye11,12
f. Nerve cells, including the brain13
Prostaglandin Synthesis
Vitamin E modulates prostanoid or eicosanoids biosynthesis. Prostanoids are compounds derived from
polyunsaturated fatty acids and include thromboxanes, prostacyclins, leukotrienes and three series of primary prostaglandins.1 By down regulating the conversion of arachidonic acid to the pro-inflammatory prostaglandin series 2, Vitamin E supplementation has been shown to reduce inflammatory conditions and also to decrease platelet clotting, although this effect may also be attributable to Vitamin E’s ability to directly antagonize the clotting function of Vitamin K.1,14,15
Nervous system function
As Vitamin E deficiency results in nerve damage, Vitamin E is required to preserve the normal function of nerve cells.6
Male Fertility
Vitamin E deficiency or marginal deficiency can result in decreased male fertility, which can be reversed via Vitamin E
supplementation.16
Supplementation Studies and Clinical Applications
Cardiovascular Disease
Substantial evidence suggests that Vitamin E supplementation can reduce the risk of coronary heart attack, stroke, angina, peripheral vascular disease and advancing atherosclerosis. The mechanisms of protection appears to be the following:
Decreased LDL-cholesterol oxidation: decreases oxidation of LDL cholesterol and thereby, reduces its uptake by macrophages and their subsequent transformation into foam cells. Foam cells are part of the atherosclerotic plaque and represent the primary mechanism by which cholesterol becomes incorporated into the atherosclerotic process, which narrows arteries throughout the body.8,17,18
Inhibition of Excessive Platelet Aggregation: via its effects on prostaglandin synthesis, Vitamin E appears to reduce the synthesis of thromboxanes A2, which increases platelet coaguability and it has been shown to antagonize the action of Vitamin K, which is a procoagulant. Thus, Vitamin E acts like a natural blood thinner, but with far less potency than aspirin or warfarin (coumadin).1,15,19
Inhibits the Proliferation of smooth muscle to grow into the lumen of the artery: as part of the atherosclerotic process platelets release a growth factor which normally encourages smooth muscle and connective tissue to proliferate and grow into the lumen of the artery, further reducing blood flow and narrowing arteries. Vitamin E has been shown to inhibit smooth muscle proliferation in experimental studies.20,21
Heart Disease Studies: a number of large prospective studies have demonstrated that Vitamin E supplementation of 100 I.U. or more is associated with approximately a 40 percent reduction in risk of heart disease compared to subjects not taking Vitamin E supplements or supplementing at a dosage below 100 I.U. per day.22,23,24
Intervention trials with high risk heart disease patients have also revealed that the use of Vitamin E supplementation of 100 IU or more per day, significantly reduced risk of heart disease, heart attack and fatal myocardial infarction. In the Cholesterol Lowering Atherosclerosis Study of 156 men (age 40-59) post bypass surgery, 100 IU or more of Vitamin E per day significantly decreased restenosis of coronary arteries, as evidenced by angiography studies after several years of follow-up.25
In the Cambridge Heart Antioxidant Study (CHAOS) supplementation with 400 or 800 I.U. of Vitamin E reduced risk of non-fatal heart attacks by 75 percent in high-risk patients as compared to those given the placebo. The beneficial effects were apparent after one year.26 The Finnish Alpha-Tocopheral, Beta-Carotene Cancer Prevention Study (ATBC) also showed a reduction in heart disease in subjects taking Vitamin E supplements compared to the placebo group.27 However, Vitamin E supplementation showed no benefit in the Heart Outcomes Prevention Evaluation Study.28
Angina: in the ATBC study mentioned above, Vitamin E supplement users also demonstrated a reduction in angina.27 Other studies have shown that Vitamin E has been effective in patients with existing angina pectoris.20,29 Intermittent Claudication: intermittent claudication has also been improved with Vitamin E supplementation.20,30-33
Alzheimer’s Disease
Emerging evidence links free radical damage to brain cells with the development and progression of dementia and Alzheimer’s disease. In the Alzheimer’s Disease Cooperative Study a daily dosage of 2,000 I.U. of Vitamin E slowed the functional deterioration of Alzheimer’s patients. Vitamin E appears to protect nerve cells from A beta-amyloid protein-induced oxidative damage and neurotoxicity.13,34,35
Prostate Cancer Prevention
Subjects in the ATBC study (mentioned above) taking 50 mg of Vitamin E (75 I.U.) showed a 32 percent decrease in the incidence of prostate cancer and a 41 percent decrease in prostate cancer death, compared to those taking the placebo.36
Post Cancer Treatment
In the study by Lockwood a cocktail of antioxidant supplements (including Vitamin E-2,500 I.U.) and other nutrients reduced the progression of breast cancer in women with existing axillary lymph node involvement.37
Primary Cancer Prevention
Results from the US National Institute on Aging study showed a 22 percent decrease in risk of cancer death compared to non-Vitamin E supplement users.38
Vitamin E exhibits a number of cancer prevention effects beyond antioxidant function, which include antiproliferative and apoptosis (programmed cell death) effects on certain human cancer cell lines as well as other protective functions.39-42
In the Iowa Women’s Health Study women with the highest intake of Vitamin E (primarily supplementation) had a 30 percent lower incidence of colon cancer compared to those demonstrating a low Vitamin E intake.43 Similar findings exist for cervical cancer (40 percent reduction in risk with high Vitamin E intake).44
The Iowa Women’s Health Study has more recently demonstrated that higher Vitamin E intake may also reduce risk of oral, pharyngeal, esophageal and gastric cancers.45 Vitamin E also blocks the formation of cancer causing nitrosamines in the human intestinal tract,68 in a similar fashion as Vitamin C.
Fibrocystic Breast Disease
Some studies have shown that 600 I.U. of Vitamin E taken as a supplement can reverse fibrocystic breast disease.46,47
Cataracts and Macular Degeneration
Several preliminary studies reveal that Vitamin E supplementation (usually in combination with other antioxidants) can reduce the risk of cataracts and halt or slow the progression of macular degeneration of the eye (some cases showed improved visual acuity) in intervention trials.48,49,50
Male Fertility
In one study infertile males (n=52) treated with 600-800 I.U. of Vitamin E demonstrated improvement in sperm quality; eleven were able to impregnate their spouses following Vitamin E treatment.51
Tardive Dyskinesia
Drugs that treat schizophrenia may trigger Tardive Dyskinesia due possibly to free radical damage to nerve cells. Vitamin E supplementation at 1,600 I.U. has been used successfully to treat Tardive Dyskinesia in these patients.52,53,54
HIV/AIDS
A nine year study involving 311 HIV-positive men showed that those patients with highest Vitamin E intakes had a 35 percent decrease in risk of progression to AIDS when compared to the lower intake group.55 Other studies suggest a similar protective effect.56,57
Hepatitis C
A 1997 preliminary study of 23 hepatitis C patients treated with 400 I.U. of Vitamin E, twice per day, revealed significant improvement in 11 of 23 patients as demonstrated by clinical testing of liver function.58
Asthma
A preliminary study has shown that supplementation with 400 I.U. of Vitamin E and 500 mg of Vitamin C increased peak flow capacity by 18 percent in a trial of 17 asthma sufferers (treadmill testing with peak flow lung function tests).59
Rheumatoid Arthritis and Osteoarthritis
Several studies have shown that Vitamin E supplementation at 400 I.U. per day or 895 IU, twice per day can reduce symptoms and signs of rheumatoid arthritis, when compared to placebo.14,60
Osteoarthritic patients have also shown benefit from Vitamin E supplementation.61,62
Diabetes
Vitamin E supplementation has been shown to improve insulin sensitivity (900 I.U. per day) in elderly subjects, as well as fasting glucose, triglycerides and LDL:HDL ratio.63 Vitamin E supplementation of 100 I.U. per day significantly lowered lipid peroxidation products and lipid levels in diabetic patients.64
Exercise-Induced Free Radical Damage
Studies are demonstrating that Vitamin E daily supplementation (400 I.U to 1,200 I.U.) reduces free radical damage induced by aerobic and strength training exercise, preserving muscle membrane structure and reducing muscle inflammation.65
Diabetes
Vitamin E studies with diabetic patients have generally revealed a number of significant benefits, which include:
Decreased LDL-Cholesterol oxidation
Improved insulin sensitivity
Lower triglycerides
Improved LDL:HDL ratio
Improved glucose tolerance
Lower fasting insulin levels.
In two trials, a daily dosage of 1,350 I.U. of Vitamin E was used for up to 4 months.66,67 However, in one trial a dosage as low as 100 I.U. per day of Vitamin E was shown to significantly lower lipid peroxidation and lipid levels over a three month period.64
Premenstrual Syndrome
Vitamin E supplementation (400 I.U.) has been shown to improve various symptoms in PMS. In one double-blind trial a success rate of 33 percent was realized with respect to physical symptoms, and 38 percent with anxiety.68,69
Parkinson’s Disease
Oxidative damage has been shown to be a contributing factor to Parkinson’s disease. A preliminary study demonstrated that Vitamin E supplementation significantly showed the progression of the disease. More recently, a double-blind study showed no benefit with Vitamin E supplementation. Further trials are underway.70,71
Restless Leg Syndrome
Vitamin E supplementation has been shown to be useful in some studies.72,73
For most conditions reviewed above, Vitamin E supplementation of 100-400 I.U. has been shown to provide the stated benefits. Higher doses have been used in the following cases:
Dosage Ranges
Adverse Side Effect and Toxicity
Vitamin E exhibits very little toxicity, even at high doses (i.e., 3,200 I.U. per day) in two-year trails.75 At doses higher than 800 I.U. per day, Vitamin E may increase the risk of a bleeding disorder. At higher doses it may infrequently cause high blood pressure, and abdominal pain.76
Increasing the dosage slowly over time may overcome the high blood pressure response that occurs in some patients (Author’s note). Begin at 100 I.U. per day.
Drug-Nutrient Interactions
Vitamin E supplementation can potentiate the anti-coagulant effect of aspirin, warfarin or coumadin at does above 400 I.U. In this case, a bleeding disorder may result. The general consensus is that Vitamin E at a daily dosage up to 400 I.U. can be taken concurrently with these medications.77,78
Drugs that deplete Vitamin E include:
Bile Acid Sequestrants
Gemfibrozil
Isoniazid
Mineral oil
Anticonvulsants (phenytoin, carbamazepine and Phenobarbital)
Orlistat - decreases Vitamin E absorption
Chitosan - decreases Vitamin E absorption if taken at the same time79-89
Vitamin E can serve a supportive interaction with the following drugs:
Allopurinol Cycolsporin Griseofulvin Simvastatin Sodium fluoride90
Neomycin impairs utilization of Vitamin E. Vitamin E can help reduce the side effects of the following drugs:
Amiodarone
Anthralin
Benzamycin
Chemotherapy
Cyclophosphamide
Dapsone
Haloperidol
Lindane
Risperidone76,90
High intakes of polyunsaturated fats can decrease Vitamin E levels in the body, thus increasing Vitamin E requirements.1
Pregnancy and Lactation
During pregnancy and lactation, the only supplements that are considered safe include standard prenatal vitamin and mineral supplements. All other supplements or dose alterations may pose a threat to the developing fetus and there is generally insufficient evidence at this time to determine an absolute level of safety for most dietary supplements other than a prenatal supplement. Any supplementation practices beyond a prenatal supplement should involve the cooperation of the attending physician (i.e., magnesium and the treatment of preeclampsia.)
References: Pregnancy and Lactation
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